Fatigue is another culprit.
Once the offense gets 1 or 2 completions, the DL is physically spent and no longer gets pressure. This is made worse by the offense's hurry up mode.
The key is to keep the offense out of that rhythm.
Forcing incompletions is a way to do that, but that's hard to do when you're sitting in a soft zone.
For some reason, DCs lose sight of that very obvious fact and they rely too heavily on the clock, but that's a relic of yesteryear.
Offenses today can, and do, score TDs in under 40 seconds. The Chiefs got into FG range in 13 seconds.